Polyether polyols and nonionic surfactants are prepared by means well known in the art. Generally, they are prepared by the reaction of alkylene oxides with starter molecules that have active hydrogens. The reaction is often catalyzed with alkaline catalysts. At the end of the reaction it is desirable to deactivate the catalyst by either removing or neutralizing it. A common method of catalyst removal is by treatment with magnesium silicate and subsequent filtration. In other cases the alkaline catalyst is neutralized with an inorganic acid to precipitate the salts which are filtered with or without further treatment with magnesium silicate. However, the most cost-effective way of deactivating the catalyst is by neutralizing with an acid and leaving the salt in the nonionic surfactant. The most commonly used catalysts in the preparation of nonionic surfactants are potassium and sodium hydroxides, and the most commonly used neutralizing acids are acetic, sulfuric, and phosphoric acids. Hypophosphorous acid is also used.
A disadvantage with neutralizing with an acid and leaving the salt in the polyether polyol or nonionic surfactant (the two terms are used interchangeably in the discussion which follows) composition arises where the salt is not soluble in the polyol. In such a case, the salt generated by the neutralization process will show up as a haze or precipitate. Precipitation of the salt in the product creates problems in storage tanks, filter pumps and lines. Further, the salt creates disposal problems and product loss by absorption. Even though most of the salt can be removed by bag filtration at the point of manufacture, crystallization is a slow process and so salts can crystallize and precipitate after shipment. This final crystallization of the salt in the polyether polyol fouls feed equipment resulting in equipment damage and loss of product flow to the process stream. Filtration and removal of the catalyst by the aforementioned magnesium silicate procedure is not cost effective since the filter cake has to be disposed of and there is product loss by absorption onto the magnesium silicate. The most cost-effective way therefore, is to neutralize the nonionic surfactants with an acid, which gives soluble salts, and to leave the salt in the nonionic surfactant.
The art has experimented with ways to neutralize nonionic surfactant products by using different acids as neutralizing agents. U.S. Pat. No. 4,430,490 discloses the use of hydroxy carboxylic acids to form a clear reaction mixture without otherwise removing the alkaline catalyst. The polyether polyols are said to be useful for the production of polyurethane foams. U.S. Pat. No. 4,426,301 discloses the use of certain benzoic acid derivatives (such as e.g. salicylic acid) as a neutralizing agent for polyoxyalkylene surfactants (both monool and polyol) having greater than 50% ethylene oxide units. While these acids gave clear products, the hydroxy benzoic acids are solids and encounter process difficulties in their incorporation. Further, the neutralized polyoxyalkylene surfactants may generate a pink color when neutralized with hydroxy benzoic acids. Finally, the use of hydroxy carboxylic acids such as lactic acid introduces hydroxyl functionality into the neutralized polyether polyol. The increased hydroxyl functionality may lead to off spec material due to a too high hydroxyl number, or may interfere with applications of the polyols, as for example in polyurethanes when there is to be a subsequent reaction of hydroxyl groups on the polyol with isocyanate groups.
Applicants have now discovered that a class of branched aliphatic acids, which overcomes the disadvantages of the known acids discussed above, is useful for neutralizing polyether polyols. The salts of neutralization may be left in the polyether polyol product, sparing the expense of catalyst removal by absorption and/or filtration. The acids are generally liquids at room temperature, and are of low viscosity for ease of handling. They are relatively odor free and have a low order of toxicity. These acids give clear products with no settlement of salts when used to neutralize the alkaline catalyst after polymerization of alkylene oxides onto starter molecules. Essentially, the neutralized salts of these acids are soluble in the polyether polyol. Because there is no precipitate, there is no accumulation of crystallized salt, and equipment clean up is not required due to the accumulation of crystallized salt. Furthermore, the flow of the product to the process stream is not obstructed by the accumulated salt. Finally, the organic acids of the invention do not contribute to hydroxyl number of the final product, and do not interfere in subsequent reactions of the polyol.